1. Field of the Invention
The invention relates to an improved fluid delivery system where quick, effective flow interruption is critical, and is particularly directed to a system for more accurately controlling the amount of dampening fluid delivered to the plate cylinder of an offset printing press for improvement of print quality.
2. Description of the Prior Art
In the offset printing press, a small amount of a dampening solution, i.e., water with certain additives, is supplied to the offset plate carried on a plate cylinder, which then comes in contact with the inking rollers, the ink adhering to the image on the plate and the dampening solution adhering to the other portions of the plate. The quantity and placement of the dampening solution must be varied for different types and densities of ink, variations in printing densities and coverages, and press speeds. Control of the application of the dampening fluid is particularly important in four-color processes, where variations will affect color. If too little fluid is applied, printing will occur in areas where none is desired. If too much fluid is applied, printing may not occur in some areas, and scumming may also occur.
Over the years, a number of systems have been developed which are directed to the problem of accurately controlling the flow of the dampening solution onto the offset plate. For example, my previously issued U.S. Pat. No. 4,064,801, assigned to the present assignee, discloses a system which keeps the fluid supply under pressure without employing a liquid pump, whereby the amount of air drawn into the fluid supply is minimized and, hence, the formation of small air bubbles which interfere with the pumping action and cause imprecise application of the dampening fluid is eliminated. My previously issued U.S. Pat. No. 3,508,711, also assigned to the present assignee, teaches the use of a single fluid control unit to supply fluid at determined intervals through a single line to a spray head manifold having a plurality of spray nozzles which are individually operated in response to fluid pressure. U.S. Pat. No. 3,949,668, issued to R. Smith, discloses means for minimizing drippage subsequent to shutoff by utilizing a separate piston for each outlet line and accompanying spray nozzle. Each of these patents is fully incorporated by reference in this disclosure.